Generally, most of various devices for countermeasure on exhaust gas in an automobile normally operate in a condition of an engine being sufficiently warm. With respect to, for example, a so-called EGR device in which part of exhaust gas extracted from an exhaust side is cooled by an EGR cooler and is returned to an intake side, the exhaust gas returned to the intake side suppressing combustion of fuel in an engine to lower a combustion temperature to thereby reduce generation of NOx, control is conducted in a condition of the cold engine at cold start thereof (cold condition) such that warming of the engine is prioritized with recirculation of the exhaust gas being stopped. Whether the engine becomes sufficiently warm or not is determined by detecting a temperature of cooling water having passed through the engine by a water-temperature sensor.
Further, monitored is whether the detection value of the water-temperature sensor is within a normal range or not. When the detection value becomes out of the normal range into a value impossible in normal use, abnormality of the water-temperature sensor is determined to reject the detection value of the water-temperature sensor and temporarily employ a fixed substitute value while stopped is a device operating in dependence upon a temperature of cooling water such as an EGR device for recirculation of exhaust gas.
Explanation is made on, for example, an EGR device. If recirculation of exhaust gas were started to an unwarmed engine still in cold, low-temperature exhaust gas having passed through an EGR cooler would be introduced into the cold engine, resulting in generation of while smoke. Thus, taken is action of stopping the EGR device so far as the water-temperature sensor is indicative of abnormality.
Stopping action is similarly taken on a device other than the EGR device which operates in dependence upon a temperature of cooling water since the device cannot normally operate in such condition; with respect to specifically trouble-free control, a fixed substitute value is temporarily applied as temperature of the cooling water to continue the control.
There exists, for example, the following Patent Literature 1 as conventional art document pertinent to such determination of abnormality on a water-temperature sensor.